This invention relates to a method for confirming whether the data transmitted from a head end unit is accurately transmitted or not to a terminal unit in a bidirectional CATV system and also to a terminal unit directly used for carrying out its method.
In conventional bidirectional CATV systems heretofore proposed, commands from the head end and other data are interpreted at the terminal unit and the function of the terminal unit is controlled according to these data. The operating state of the terminal unit such as, for example, which channel is looked at and listened to, whether the picture of a channel which should be scrambled so that its picture cannot be watched unless a special contract is agreed to is actually scrambled or not, is detected by various detecting means and the data are fed to the head end. However, it cannot be checked nor confirmed at the head end whether the terminal unit is functionally prepared to scramble the picture or not, for example, when a subscriber not specially contracted as above intends to look at a restricted access channel while the subscriber is watching a different, no charge, channel. Thus, it does not have a function enabling it to check at any time the current status of the terminal unit and whether such command has been positively transmitted to and acted upon by the terminal unit.
It is, therefore, one object of the present invention to provide a method for confirming transmission in a bidirectional CATV system which eliminates the aforementioned disadvantages of the conventional bidirectional CATV system and which can confirm at the head end any time whether the command or other data fed from the head end has been accurately transmitted to the terminal unit or not.
It is another object of the present invention to provide a terminal unit in a bidirectional CATV system which has a function to confirm any time at the head end whether the command or other data fed from the head end is accurately transmitted to the terminal unit or not.